JPS6239107B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermal recording device used in facsimile machines, etc., and in particular to a thermal recording device for keeping the recording density constant by controlling the current application time for recording subsequent image information according to the preceding image information. The present invention relates to a heat-sensitive recording device as described above.

A thermal recording device uses a heating element made of a resistor as a recording element, which is energized according to the image information, and the heat generated is used to record on thermal paper.It is easy to maintain and can be used for clean recording, etc. However, it has a drawback in terms of recording speed in fields of use such as facsimile. In other words, since heating elements have a heat storage effect, if the same heating element is repeatedly energized two or more times in succession, and if the interval between energizations is shortened to increase the recording speed, the temperature of the heating element will rise and recording will be interrupted. The concentration will increase. Therefore, after recording the preceding image information, when recording the subsequent image information, the heat accumulation around the heating element is simulated by charging and discharging the capacitor.
Attempts have been made to keep the recording density constant by controlling the energization time of the heating elements accordingly. This principle will be explained using FIG. 1.

In FIG. 1, the time constant of the terminal voltage of capacitor C due to RC is set equal to the thermal time constant of the heating element. First, to record image information,
At the same time as applying a voltage to the heating element, a constant voltage V _p is also applied to the terminal 1. The comparator 3 detects the point in time when the terminal voltage of the capacitor C becomes equal to the reference voltage V _ref applied to the terminal 2, and the time when the terminal voltage of the capacitor C becomes equal to the reference voltage V ref applied to the terminal 2 is detected, and the heating element is energized from the terminal 4 and the voltage V to the terminal 1 is turned on.
The energization time of the heating element is controlled by issuing a signal to stop the supply of _p . That is, by keeping the peak of the terminal voltage of the capacitor C constant, the temperature peak of the heating element is also kept constant.

However, in this method, the thermal time constant of the heating element is
Despite the fact that the amount of heat generated due to energization is smaller than that generated during cooling due to rest, and this tendency becomes more pronounced as the recording speed increases, the time constant of the terminal voltage of capacitor C due to RC is is constant, so the above simulation does not give a good approximation, especially when recording at high speeds. This will be specifically explained using FIG. 2. Figure 2 shows the change in terminal voltage of capacitor C 11 and the temperature change of the heating element 12 when the time constant by RC is set equal to the time constant when the heating element heats up, and the temperature controlled by the circuit in Figure 1. This shows the energization time 13. The peak of the output voltage of the capacitor is constant as shown in 11', but the temperature of the heating element is 11' because the thermal time constant during cooling is large and heat dissipation is insufficient.
In the second energization as shown in 2', the peak rises. Therefore, the recording density also increases accordingly. Furthermore, since the circuit shown in FIG. 1 is an analog circuit, it also has the disadvantage that adjustment when setting the time constant using RC is complicated.

This invention has been made in view of the above-mentioned drawbacks, and provides a thermal recording device that maintains the recording density of preceding image information and subsequent image information constant regardless of the recording speed, and that can be easily adjusted during use. It is intended to.

The present invention establishes the ideal relationship between the time interval between the preceding image information and the following image information and the energization time of the heating element for recording the subsequent image information with the same density as the preceding image information. Obtain by measuring the recording density, approximate this correspondence with a polygonal line that is a collection of two or more linear relationships, and control the energization time according to the above-mentioned time interval based on this correspondence. The main point is In this way, the measurement results of the actual recording density can be used to determine the energization time, so the difference in physical constants such as time constants between the simulation model and the actual heating element It is possible to eliminate the universal error in the determined value of the energization time that occurs, and to obtain a stable and good approximation in any situation, which not only avoids unilateral increases and decreases in recording density, but also allows linear relationships. By using a combination of the above, the entire circuit configuration can be digitized, and the labor for circuit adjustment can be greatly reduced.

Hereinafter, the present invention will be specifically explained with reference to Examples.

FIG. 3 shows an outline of an embodiment of the present invention, in which image information to be recorded (for example, an image signal in a facsimile) is input serially one line at a time to a terminal 21, and is read into a shift register 22. . When this reading is completed, the energization time control circuit 27, which will be described later, sets τ for the energization time control.
A logic “1” level control pulse with a time width (variable) _of A logical sum is taken. Then, at the AND gate 28, the output of the OR gate 26 and the output of the shift register 22,
The AND gate 2 is logically ANDed with a logic "1" level pulse having a time width (fixed) of τ _n to give the maximum energization time input to the terminal 29.
The output of No. 8 is given to the power source 30 as a energizing pulse to the drive circuit 32 connected in series with each heating element 31, thereby energizing the heating element 31 and recording image information for one line. In this case, the time width of the energization pulse given to the drive circuit 32, that is, the energization time of the heating element 31, is _τ
The "0" bit will be set to τ _n . Then, a latch pulse is input to the terminal 23, and the contents of the shift register 22 are transferred to the latch circuit 24.
The image information for the next line is then transferred to a recording standby state.

Next, the energization time control circuit 27 will be explained. Figure 4 shows the relationship between the time interval T between the preceding image information and the following image information and the energization time τ of the heating element to record the subsequent image information with the same density as the preceding image information. The curve 41 represents an ideal relationship based on actual measurements, and the polygonal line 42 represents an approximation of the curve 41 by a combination of three linear relationships. T _p is the minimum value of the time interval T during actual use, and T _n is a value at which control of the energization time τ by the time interval T is stopped. Also, τ _p and τ _n are T _p and T _n
, and τ _n is equal to the time width of the pulse input to the terminal 29 . T ₁ and T ₂ are the time intervals of the bending points of the polygonal line 42, that is, the points where the linear relationship changes, and the time interval T is divided into the three time regions 43, 44, and 45 by T ₀ , T ₁ , and T ₂ . , and each has its own linear relationship with the energization time τ. τ ₁ and τ ₂ are energization times corresponding to T ₁ and T ₂ .

Now, as an example, if _{we consider the case where subsequent image information arrives at a time interval corresponding to T x in FIG .} According _{to the} linear relationship _between T _{and τ} , _{which is} unique _to controlled like _x .

Figure 5 shows the energization time control circuit 2 based on this principle.
7 shows a specific example of the configuration. In FIG. 5, a signal indicating a time interval T _x , that is, a pulse train having an interval of T _x is inputted to a terminal 51 . This pulse is a synchronization signal inserted at the beginning of each line, for example, when the image information is a facsimile image signal. A first counting circuit, for example a counter 53, is set by this pulse and measures the time interval T _x by counting the clock pulses of constant period do input from the terminal 52. The time interval T _x of this first counter 53
Output data indicating
A preset type second counting circuit, e.g. counter 5
5 are output in parallel. The second counter 55 is preset with the parallel output from the latch circuit 54 as an initial value by the load signal input from the terminal 56, and counts clock pulses with a period d (variable) output from the clock generation circuit 57. .
When the content of the second counter 55 reaches a certain value, for example "0", a carry-out signal is output to the control pulse generation circuit 58.

Here, as the time interval T increases, the period d of the clock pulse output from the clock generation circuit 57, the period up to T ₁ in FIG. 4 is d=do×(τ ₁ −τ ₀ )/T ₁ ...(2) The period from T ₁ to T ₂ is d = do × (τ ₁ - τ ₂ ) / (T ₁ - T ₂ ) ... (3) The period from T ₂ to T _n is d = do × (τ _n -τ ₂ )/(T _n -T ₂ ) ... (4) If it is changed as shown in (4), the carry-out signal from the second counter 55 will be changed from the timing of the load signal input from the terminal 56. It is output after a time of (τ _x −τ ₀ ). Now, after a time interval T _x from the preceding image information, from the input timing of the pulse that informs the arrival of the subsequent image information to the terminal 51
If you input the load signal after ₀ time elapses,
The carry-out signal is output after a time τ _x has elapsed from the input timing of the pulse to the terminal 51.
Then, the control pulse generating circuit 58 generates a pulse with a time width τ _x corresponding to the time interval between this carry-out signal and the pulse to the terminal 51, and generates a pulse with a time width τ _x corresponding to the time interval between the carry-out signal and the pulse to the terminal 51. It is output to terminal 59 as a control pulse.

FIG. 6 shows an example of the configuration of the clock generation circuit 57, and 60 is a terminal 6 to which the carry-out signal S60 from the second counter 55 is input.
1, 62, and 63 are respectively ~ _{T 1} , T ₁ ~T ₂ , T ₂ ~
R-S flip-flops 63', 64, and 65, which output signals specifying the period _Tn , are controlled by flip-flops 61, 62, and 63, and terminals 66,
The periods input to 67 and 68 are d=
do×(τ ₁ −τ ₀ )/T ₁ , d=do×(τ ₁ −τ
₂ )/(T ₁ −T ₂ ), d=do×(τ _n −τ ₂ )/(T
The AND gate 69 outputs a pulse of _n − T ₂ ) during the period of ~T ₁ , T ₁ ~ _{T 2} , T ₂ ~T _n
The output pulse of the OR gate 69 is outputted to a terminal 70 as a clock pulse with the previous period d, and is also inputted to a counting circuit, for example, a counter 71. The counter 71 receives the second input signal to the terminal 60.
It is set by the carry-out signal from the counter 55, and the output pulses of the OR gate 69 are counted to generate timing signals T ₁ and T ₂ to be applied to the flip-flops 61, 62, and 63.

As explained above, according to the present invention, it is possible to control the energization time corresponding to the time interval at which image information arrives in order to record image information at a constant density using only a digital circuit. It is easy to adjust after. Furthermore, since the simulation characteristics do not depend on electrical or mechanical means, errors due to approximation will not be biased to one side.
Furthermore, by increasing or decreasing the slope of the polygonal line, the linear relationship to be used can be arbitrarily increased or decreased, so it is possible to easily increase or decrease the accuracy of controlling the current application time to keep the recording density constant.

The present invention is not limited to the above-mentioned embodiment. For example, a polygonal line approximation may be used as a specific method for controlling the energization time for recording image information at a constant density based on the time interval of image information arrival. Correspondence between time interval and energization time by approximation
It is also possible to store it in ROM.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a current-carrying time control circuit for keeping the recording density constant according to the conventional method, FIG. 2 is a diagram for explaining the operation of FIG. 1, and FIG. 3 is an embodiment of the present invention. 4th block diagram of the thermal recording device according to
The figure is a diagram showing the relationship between the time interval of arrival of image information and the energization time to keep the recording density constant to explain its operation, and FIG. 5 is a specific configuration example of the energization time control circuit in the same embodiment. FIG. 6 is a block diagram of the clock generation circuit in FIG. 5. 21... Image information input terminal, 22... Shift register, 24... Latch circuit, 27... Energization time control circuit, 31... Heat generating element, 32... Drive circuit,
51... Image information arrival time interval pulse input terminal, 5
2...Clock pulse input terminal with constant cycle, 53
...First counter, 54...Latch circuit, 55
...Second counter (preset counter), 5
6... Load signal input terminal, 57... Variable cycle clock pulse generation circuit, 58... Control pulse generation circuit, 59... Control pulse output terminal.

Claims (1)

[Scope of Claims] 1. A thermal recording device that records image information on thermal paper by energizing a heating element to generate heat in accordance with image information that is repeatedly input. By counting the first clock pulses of a constant period from the time when one of the pulses inserted at the head position of the line is input to the time when the next said pulse is input, the preceding image information and the following image information are calculated. a first counting circuit for measuring the time interval with the clock information; and a second counting circuit for counting the second clock pulses having a variable period, in which output data indicating the time interval of the first counting circuit is given as an initial value. a counting circuit; a circuit that changes the period of the clock pulse every time a predetermined number of clock pulses inputted to the second counting circuit is counted; 1. A thermal recording device comprising: a circuit for generating a control pulse for controlling an energization time for recording subsequent image information based on timing; and an energization time control circuit.